Ecosystem changes in Galápagos highlands by the invasive tree Cinchona pubescens

Abstract

Background and aims Various studies address changes in nitrogen and carbon cycling by exotic plant species, while impacts on phosphorus cycling are understudied. Therefore, we assessed the effects of the introduced Cinchona pubescens Vahl on plant and soil nutrients (especially phosphorus) in the highlands of Santa Cruz Island, Galapagos. Methods Nutrient analyses were carried out on soil, leaf litter, and leaf samples taken from Cinchona, the endemic shrub Miconia robinsoniana Cogn. and the native fern Pteridium arachnoideum (Kaulf.) Maxon. in plots invaded and previously invaded by Cinchona. Results Cinchona contained significantly more nitrogen, phosphorus and potassium in its green leaves than Miconia. Surprisingly, there was no evidence of phosphorusresorptioninsenescedCinchonaleaves.Thiswas also the case in Miconia leaves, but only in Cinchonainvaded plots. Specific leaf area of Cinchona was significantly higher than of Miconia and Pteridium leaves, as was its litter turnover rate. Total soil nitrogen, ammonium andavailablephosphorusconcentrationswerehigher in the invaded plots. Leaf litter from these plots also contained more phosphorus, which was positively correlated with the phosphorus concentrations in the soil. Conclusions These results suggest enhanced nutrient uptake by Cinchona and a faster decomposition of its litter, leading to increased nutrient availability in the soil. An accelerated cycling could promote spread of Cinchona and other introduced species, increasing the risk of further displacement of indigenous plant species in the Santa Cruz highlands.